Kohlrabi, scientific name Brassica oleracea Gongylodes group, is also known as German turnip. It is a low, stout swollen stemmed cultivar of cabbage that can be grown almost anywhere.
The plant got its name from the German Kohl and turnip because of its features and taste. It is mainly grown as a spring crop, but can also be sown and transplanted in the summer for an autumn harvest.
Kohlrabi photograph by Jorge Andrade (CC: https://www.flickr.com/photos/viajor/)
Different varieties include Early Purple Vienna (can be harvested within 60 days); Purple Danube (52 days); Grand Duke (50 days); and Early White Vienna (55 days).
As they are all bred from the same species (Brassica oleracea), Kohlrabi's origin in nature are highly similar to those of broccolib, cabbages, Kale, cauliflower, Brussels sprouts, and collard greens.
The plant's texture are similar to those of a cabbage heart and broccoli stem but the taste is sweeter and milder similar to that of a turnip. Its young stem can be as juicy and crisp as an apple but not nearly as sweet. Kohlrabi is highly nutritious and makes an excellent source of fiber, potassium, and vitamin C. A single cup of this leafy green contains 40 calories. In addition to its health benefits, Kohlrabi can also be grown as a distinctive ornamental plant in outdoor containers.
This leafy vegetable is a hardy biennial plant that is grown as an annual. It has a stem that is swollen and globe-shaped that makes it looks like it is a turnip that grows on a cabbage root. The stems can be green, purple, or white, and is topped with a rosette of long, blue-green leaves. Plants are easy to maintain and typically range from 12 to 18 inches (30 – 45 cm) in height, with a similar spread.
Choose a location that has full sun with good drainage and a fertile soil that is rich in organic matter. It is best to prepare the beds and add aged compost two to three weeks before planting. The ideal soil pH should be around 5.5 to 6.8, although it can also tolerate slightly alkaline soil up to pH 7.5.
Kohlrabi is a heavy feeder, and requires regular watering to keep the soil constantly moist. Do not grow in deep soil as the stems will grow into bulbs.
Kohlrabi plant leaves by B.D.'s world (CC: https://www.flickr.com/photos/bdsworld/)
Kohlrabi is a cool-weather crop, so it is best to sow the seeds in the garden three to four weeks prior to the last average frost date in spring. Germination occurs in soil temperatures of 40 to 80°F (4.5 – 26°C) and takes from 4 – 7 days. The plant needs 45 to 60 days to reach harvest, with temperature not exceeding 75°F (24°C).
Kohlrabi can also be sown in late summer for a winter harvest in warmer regions as the plant can withstand an early autumn frost, but in cold winter regions it is best to sow the plant earlier in the summer for an early autumn harvest.
Sow the seeds ½ inch (1.2 cm) deep with a one inch (2.5 cm) spacing. Rows should be spaced at 12 to 24 inches (30 – 60 cm). Thin successful seedlings to five to eight inches (13 – 20 cm) apart.
For a faster growth, keep the soil evenly moist as a kohlrabi plant without sufficient water will normally turn woody. Preparing planting beds two to three weeks before sowing or transplanting and adding organic fertilizer are beneficial. Side dress the plant with aged compost during the midseason.
Careful cultivation is advised to prevent damaging the shallow roots. When the plants are four to five inches tall, mulch kohlrabi with aged compost as cold temperatures can cause kohlrabi plants to bolt.
The kohlrabi plant can be attacked by cabbage loopers, cutworms, flea beetles, cabbage aphids, and imported cabbage worms. Spraying bacillus thuringiensis can help to control cabbage worms. Placing collars around the stem can give aid in protecting seedlings form cutworm damages. Carefully remove egg clusters, which are normally found underneath the leaves, and wash the plant with a diluted soap solution.
The kohlrabi plant is susceptible to black rot, black leg, downy mildew, clubroot, and cabbage yellows. Carefully remove or destroy any infected plants.
Kohlrabi can be harvested for fresh use once the stems are two to three inches (5 – 8 cm) in diameter. Allow stems to reach four to five inches (10 – 12.5 cm) in diameter for storage purposes. Trim and clean the leaves. Kohlrabi can be stored in the refrigerator for one to two weeks, and for up to two months when kept in a cool, moist place.
This green leafy vegetable can also be frozen. Seeds will keep for about four years.